1. Field of the Invention
The present invention relates to a semiconductor device and to a method of fabricating the device; and more particularly to a semiconductor device on which dummy patterns are formed on a wiring layer and to the method of fabricating the device.
2. Description of the Related Art
In a conventional method of fabricating a semiconductor device having a multiple interconnection layers, when a method is adopted in which a wiring layer is formed by filling trenches with a metal, CMP (Chemical Mechanical Polishing) is used to remove unnecessary metal except the metal that has been embedded in the trenches. In such a case, a wiring pattern that has been formed unevenly on the wafer will cause variation in the polishing speed, and a countermeasure therefore is necessary for limiting variation in the film thickness of the wiring that is finally formed. For this purpose, a method has been conventionally adopted in which dummy patterns are arranged on the normal wiring layer. The dummy patterns referred to here are wiring patterns that are formed in scattered areas as a pseudo wiring pattern simultaneously with the wiring pattern, and moreover, by the same method as the wiring pattern.
The easiest and most typical method of generating a dummy wiring pattern on data involves arranging uniform dummy patterns over the entire surface of pattern data and then removing the unnecessary dummy patterns based on a logical operation with the actual wiring pattern. This type of logical operation method is described in the specification of, for example, Japanese Patent No. 3128205.
FIG. 1 shows the arrangement of dummy patterns formed on a wafer in the prior art. A plurality of chip areas 1 and scribe line areas 2 that demarcate each of chip areas 1 are provided on a wafer, and dummy patterns 3 and 4 are formed in areas 1 and 2, respectively. These dummy patterns are formed as square shapes, and the dummy patterns can be evenly generated in a grid composed of 5 by 5 squares as shown in FIG. 6 (to be described hereinbelow) by successively arranging these patterns in squares next to (in the example shown in FIG. 1 and FIG. 6, to the right of) squares that are two squares away in all directions: upward, downward, to the left and to the right of a particular dummy pattern. In the following explanation, this arrangement of dummy patterns will be referred to as the “diagonally forward skipped arrangement”.
When semiconductor devices are cut from a wafer to chip size by dicing, a process is carried out in which the wafer is cut by means of a diamond cutter. The occurrence of nonuniformity in the pattern that is formed on the cutting space of this cutter causes variation in the hardness of the wafer encountered by the cutter, and this variation tends to cause loss during cutting. In particular, when the pattern is scattered, the hardness is uniform in that portion, and loss that has once occurred tends to spread over a large area, resulting in an expanded area of loss. A construction having the “diagonally forward skipped arrangement” described hereinabove entails an increased probability that the arrangement of the dummy pattern will become sparse with respect to the direction of advance of the cutter and that a greater loss will thus occur.
In addition, in the interest of improving the performance of semiconductor devices, recent years have seen the increased use of partial films having a low dielectric constant as the insulating film between wiring layers. Typically, a film having a low dielectric constant itself has a low level of hardness, and further, has a low level of adhesion to the silicon oxide films or silicon nitride films that have been used conventionally as interlayer insulating films, and the use of a film having a low dielectric constant as the insulating film between wiring layers will therefore result in more extreme loss during dicing.
The more concentrated arrangement of dummy patterns in a grid form results in dummy patterns that are arranged evenly with respect to the direction of the advance of the cutter and thus reduces the areas of loss. Nevertheless, the arrangement of dummy patterns in grid form over the entire surface of a wafer causes unevenness in the arrangement of the dummy patterns within the chip areas. This is because, in a construction in which wiring patterns of chip interior areas are arranged in one direction (vertical direction or horizontal direction) in all areas, as is normal, excessive separation will occur between areas in which the dummy patterns remain and areas in which the dummy patterns are removed as shown in FIG. 4 when the operation is performed for eliminating unnecessary patterns as described hereinabove (refer to FIGS. 2-4).